This invention relates to ink drop printing systems and more particularly to a method and means of making an improved nozzle to be used therein.
In a U.S. Pat. No. 3,683,396, there is described a method and means for designing a nozzle for an ink drop writing system. It was shown that in order to insure a most efficient transfer of power from the driving source into the drop forming mechanism, the nozzle had to be designed to provide a fluid resonance condition. If the nozzle is considered as a closed pipe, the frequency of vibration of the fluid in the pipe at which its length is an odd multiple of a quarter wave length of sound through the fluid in the pipe is the fluid resonance length and at this length results in the highest power transfer. The mechanical resonance frequency of the pipe turns out to be close to the fluid resonance frequency.
In order to stabilize the drop forming process, the variations in drive voltage requirements for the transducer that vibrates the nozzle for drop formation, must be minimized. Variations in drive voltage requirements occur usually due to variations in the acoustic coupling between the transducer and the fluid. Most nozzles make use of resonating fluid columns in order to couple energy into the fluid, but this method falters when fluid parameters change (such as temperature concentration, velocity of sound).
When a nozzle is designed to have a length at which fluid resonance occurs, it has been found that changes in the composition or temperature of the fluid throws the nozzle out of fluid resonance, thereby causing a considerable increase in the driving power required and also to a certain extent altering the location at which drop separation from the ink stream occurs. This latter phenomenon can be significant since it is necessary to apply a charge to the drops at the location at which drop separation from the ink stream takes place.
In a U.S. Pat. No. 3,771,568, it was shown that where ink is recirculated, in order to maintain the desired fluid resonance, it was necessary to compensate for the effects of evaporation on the ink parameters.
When the composition and temperature of the ink is controlled so that fluid resonance is maintained substantially constant, no problems are encountered. However, it has been found that this is easier said than done. Users of the equipment may purchase their ink supplies from different manufacturers and therefore the fluid resonance of the nozzle which has been designed for an ink for one particular type of manufacturer is not suitable for ink of another manufacturer. Unused ink drops which are fed back into a reservoir supplying ink to the nozzle may not be compensated for the effects of evaporation as effectively as they should be. As indicated, this can adversely affect the operation of the ink drop writing system.